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From
•>>December 2004
Peter Geigenberger answers
a few questions about this month's emerging research front
in
field of Plant & Animal Science: Plant & Animal Science
Article: Starch synthesis in potato tubers is regulated by post-translational redox modification of ADP-glucose pyrophosphorylase: A novel regulatory mechanism linking starch synthesis to the sucrose supply
Authors: Tiessen, A;Hendriks, JHM;Stitt, M;Branscheid, A;Gibon, Y;Farre,
EM;Geigenberger, P
Journal: PLANT CELL, 14: (9) 2191-2213, SEP 2002
Addresses: Max Planck Inst Mol Plant Physiol, Am Muhlenberg 1, D-14476 Golm, Germany.
Max Planck Inst Mol Plant Physiol, D-14476 Golm, Germany.
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Why do you think your
paper is highly cited?
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“In our paper we present a series of experiments on potato tubers which show that these known mechanisms cannot explain how starch synthesis is inhibited when growing tubers are suddenly removed from the mother plant, and provide evidence that the inhibition is due to a novel mechanism involving post-translational regulation acting via redox-modification of ADPglucose pyrophophorylase.”
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Redox signals generated by light-dependent photosynthetic
electron transport are known to be involved in regulating the Calvin
cycle, ATP (adenosine
triphosphate) synthesis, and NADPH (Nicotinamide Adenine
Dinucleotide Phosphate Hydrogen) export from chloroplasts. Our paper
provides the first in vivo evidence that a similar mechanism
is regulating starch synthesis by post-translational redox-modification
of ADP-glucose pyrophophorylase. Our results show that redox-modulation
of this enzyme represents a component in a novel regulatory pathway
that links the rate of starch synthesis to sucrose supply. Further
components of this novel signalling pathway have to be identified
and confirmed. This opens a new way to explore sugar-signalling
pathways, since we are looking for signal transduction components
that lead to defined processes at the end of the signalling chain.
Redox-regulation might be a general concept to regulate storage
processes by sugars. This may be even the tip of the iceberg, since
recent studies by other research groups identified a large number of
proteins involved in various metabolic processes to interact with
thioredoxins using in vitro methods. It will be interesting
to determine whether this concept can also be applied to animals and
other organisms.
Does it describe a new discovery or new methodology that's
useful to others?
We provide evidence for the operation of a novel mechanism that
regulates the rate of starch synthesis in response to sugars.
According to previous knowledge, ADP-glucose pyrophosphorylase is
the key enzyme for the regulation of starch synthesis. It is
regulated transcriptionally and allosterically by metabolite
effectors. This has formed the framework for understanding how this
important process is regulated for the last 20 years. In our paper
we present a series of experiments on potato tubers which show that
these known mechanisms cannot explain how starch synthesis is
inhibited when growing tubers are suddenly removed from the mother
plant, and provide evidence that the inhibition is due to a novel
mechanism involving post-translational regulation acting via redox-modification
of ADP-glucose pyrophophorylase. We also show that this mechanism
acts in other conditions, and provide evidence that it acts to link
the rate of starch synthesis to changes in sucrose supply. It allows
the rate of starch synthesis to be changed independently of, or even
reciprocally, to changes in the levels of glycolytic intermediates.
The mechanism was overlooked in the past because it is rapidly
reversed under the standard methods used to extract and analyze
ADP-glucose pyrophosphorylase protein and activity.
Could you summarize the significance of your paper in layman's
terms?
Plants are able to synthesize sugars from inorganic carbon
dioxide during photosynthesis. The sugars are used to build up
storage compounds such as starch. We found a novel mechanism that
links the rate of starch synthesis to the sugar supply. This finding
significantly contributes to understanding the process of starch
storage in plants, which is also of central importance for human
nutrition.
How did you become involved in this research?
I became interested in the regulation of starch synthesis during
my Ph.D. thesis in Mark Stitt's laboratory at the Universities of
Bayreuth and Heidelberg. We found changes in the rate of starch
synthesis in potato tubers that could not be explained by the
current models. Supported by the German Science Foundation (DFG), I
began further investigations to find the underlying mechanisms,
which finally led to the discoveries described in this paper.
Dr. Peter Geigenberger
Research Group Leader
Storage Carbohydrate Metabolism
Max-Planck-Institute of Molecular Plant Physiology
Golm, Germany
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